Performance problem with multiple routers on same subnet

[fmatrine]

Dear Sir,

We have a WAN network with single Hub location and Multiple spoke location.

HUB location is hosting a SAP server which will be accessed by multiple Spoke locations.

We don’t have a high end Branch connectivity router which will take care of the above requirements.

We are using 1751 router (5Nos) for lease line connectivity between central location and (5Nos) remote locations.

Central site has multiple routers with each router’s ethernet terminating on a common Layer 2 switch.

My server is also placed on the same Layer 2 Switch.

Will there be any performance issue as the traffic going out of server will hit any one gateway and go to other router interface. (Server will have gateway pointing to any of the central side router ethernet interface)

Should we avoid putting gateway and put static routes in server for all the remote locations

Pls advice

[lgijssel]

For simplicity's sake you want to use a single default gateway for the entire LAN segment. You could then improve availabity by activating HSRP on it. (requires a second router also ;-)

This is the preferrable option but you have to adress two issues:

1: Use a routing protocol to correctly advertise all destination networks.

2: Enable IP redirect on the default gateway. By using IP redirect, all but the very first packet of a session is sent to the L2 address of the most suitable router. This will eliminate performance issues. ICMP takes care of sending the correct mac address to the sending host.

Regards,

Leo

[vcjones]

"Will there be any performance issue as the traffic going out of server will hit any one gateway and go to other router interface?"

If the server is sending more than one packet at a time, there will be a significant impact on performance unless all boxes are running full duplex Ethernet. The server and the router will both be trying to send at the same time, causing beaucoup de collisions and delay.

"Should we avoid putting gateway and put static routes in server for all the remote location?"

This is one way to get rid of the collisions (let the server send packets straight to the correct router). You should be able to get the same result (and may be getting it already) simply by letting your routers to send ICMP redirects and making sure your server accepts them.

Since ICMP redirects are on by default (unless you are using HSRP), you may want to investigate why they do not appear to be working. Check this FIRST, because if ICMP redirects are working, then you have a different problem. You really want to accurately determine what the problem is before wasting time fixing something which is not broken!

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

[fmatrine]

Thanks for the Guidance